With the advent of digital communications technology, many TV program streams are transmitted in digital formats. For example, Digital Satellite System (DSS), Digital Broadcast Services (DBS), and Advanced Television Standards Committee (ATSC) program streams are digitally formatted pursuant to the well-known Moving Pictures Experts Group 2 (MPEG-2) standard. The MPEG-2 standard specifies, among other things, the methodologies for video and audio data compression allowing for multiple programs, with different video and audio feeds, to be multiplexed in a transport stream traversing a single transmission channel. A digital TV receiver may be used to decode an MPEG-2 encoded transport stream, and extract the desired program therefrom.
The compressed video and audio data are typically carried by continuous elementary streams, respectively, which are broken into access units or packets, resulting in packetized elementary streams (PESs). These packets are identified by headers that contain time stamps for synchronizing, and are used to form MPEG-2 transport streams. For digital broadcasting, multiple programs and their associated PESs are multiplexed into a single transport stream. A transport stream has PES packets further subdivided into short fixed-size data packets, in which multiple programs, encoded with different clocks, can be carried. A transport stream not only includes a multiplex of audio and video PESs, but also other data such as MPEG-2 program specific information (sometimes referred to as metadata) describing the transport stream. The MPEG-2 metadata may include a program associated table (PAT) that lists every program in the transport stream. Each entry in the PAT points to an individual program map table (PMT) that lists the elementary streams making up each program. Some programs are open but some programs may be subject to conditional access (encryption), and this information (i.e., whether open or subject to conditional access) is also carried in the MPEG-2 transport stream, typically as metadata.
The aforementioned fixed-size data packets in a transport stream each carry a packet identifier (PID) code. Packets in the same elementary streams all have the same PID, so that a decoder can select the elementary stream(s) it needs and reject the remainder. Packet-continuity counters may be implemented to ensure that every packet that is needed to decode a stream is received.
Within recent years a proliferation of hand held multi-media devices have entered the market. These devices contain visual displays as well as audio outputs and connectivity to wireless Internet and intranet via, for example, IEEE 802.11n or Bluetooth® technology (registered certification mark of BLUETOOTH SIG. INC. Suite 350, 5209 Lake Washington Boulevard, Kirkland Wash. 98033, USA). Many of these devices provide methods for software developers who are not related to the manufacturer to embellish their capabilities with their own applications. Examples of such manufacturers are Apple Inc. and Google Inc. Apple provides a device called the IPOD TOUCH® (registered mark of Apple Inc., Cupertino Calif. 95014 USA) and Google provides a multiple platform operating system called ANDROID® (registered mark of Google Inc., 1600 Amphitheatre Parkway, Mountain View Calif. 94043 USA) that enables similar functionality on a plethora of devices. Cable television and Telecom Internet providers have provided household connectivity by both wired and wireless systems, such that television content can be passed between multiple internet-connected devices, which present video and audio content to their customers.
At this point, it should be noted that market research has shown that an increasing number of families have a mixture of language capability. As families migrate to the United States the younger generation learns English while the older generations remain speaking their native language. In this regard, it is known (so-called subtitles) to provide a textual representation of the words spoken in one language that are translated into another and overlaid on the television screen. Digital Versatile Disks (DVDs) may contain a selection of languages that can be presented, but only one language at a time can be played. Furthermore, museums and special exhibits have also provided multi-lingual audio devices to provide individually paced audio tours.